I have a centos 5.5 64 bit xen vps. I have a php script that automatically sends confirmation emails for people who sign up, it's not sending it right now and i believe it's because i don't have a webmail installed, right? if so then I have to install a webmail, I don't have any hosting panel.

I googled, but there's so much that I do not understand, I would like to ask about it before i install anythihg:

1- What software do you have to install in order to have a webmail?

2- Is roundcube and similar software just an interface or do they install a webmail too?

3- zimbra, postfix...what are they? are they email servers and then i have to install rouncube as an interface for them, or are they just like roundcube?

4-what is the difference between pop3 and other types of email and is pop3 the best one to use?

5- Do webmails block spams or do i have to install another software for spammers and hackers...

6- would i have to manually configure the webmail in order for it to work with my script, or not?

Note

if you answered every question I'll be so thankful, but i think it's too long, so if you don't have time to answer everything, please just answer the first question, and I'll google to get answers about the rest, or I'll ask them on other forums.

A mail server like Postfix is designed to handle sending and receiving of emails. It uses the SMTP protocol to exchange email with other email servers.

A webmail client is a collection of scripts (PHP, perl, ASP, etc) which act as a HTTP interface to a mail server, generally both an SMTP server like Postfix and also a POP/IMAP server.

Webmail is for humans. It's a user interface, like Microsoft Outlook, Thunderbird, Apple's Mail.App, Eudora, pine... etc. It has no bearing on wether PHP can send email.

To answer your specific questions:

I recommend Roundcube as a webmail client. But again, read the above, installing Roundcube won't let you send email. You want an email server, not an email client.

Roundcube is just a client. Webmail is just a client. You want an email server.

Postfix is an email server. This is what you need. Zimbra is an enture suite, containing an email server, a webmail client, a Jabber server, a web IM client, calender and contact management, browser-based document editing, and more. It's great, but, much more than what you need here.

POP and IMAP are two different ways of accessing email which has already been sent and is sitting in a user's mailbox. You don't use then to send mail, only to transfer mail from a mail server to your email client so you can read it. Which is "better" is subjective and a much longer question. I'll boil it down to this: When using POP3, email messages are removed from the server and downloaded to the email client. When using IMAP, the messages remain on the server and the email client "syncs" with the server, allowing multiple email clients (desktop system, laptop system, smartphone, etc) to check the same mailbox and all synchronize.

Generally speaking, you need spam filtering software in or before your SMTP server to block SPAM, it's not part of a webmail client. Check out SpamAssassin.

You will have to configure your email server. yes. I recommend installing Webmin, as it sounds like it may be helpful to you to have a GUI interface to configure things via. Then, Peruse the postfix questions here on ServerFault before asking more questions. Most likely, your next question ("How do I configure Postfix?") has already been asked. Keep in mind that a lot of the "configuration" of a server to make sure it can properly send emails has much more to do with DNS, reverse IPs, RFC requirements, best practices, etc than it does with actually configuring an email server to send emails.